This invention relates to a method for tinting a hydrophilic polymer employing a reactive dye.
Contact lenses of the "soft" variety are generally formed from covalently crosslinked hydrophilic polymers which are based on hydrophilic derivatives of acrylic or methacrylic acid, e.g., their hydrophilic esters or amides, hydrophilic vinylic polymers such as vinylpyrrolidone, and the like. In their hydrated state, these polymers are referred to as hydrogels, coherent three-dimensional polymer structures or networks which are capable of absorbing large quantities of water without dissolving and of transporting oxygen. In addition to hydrophilic monomer(s), the preparation of hydrophilic polymers used in the manufacture of soft contact lenses also utilizes minor amounts of less hydrophilic, and even hydrophobic, monomer(s) to confer mechanical strength and other useful properties.
Contact lenses formed from hydrophilic polymers can be tinted for cosmetic appearance as well as to reduce light transmission thereby providing the wearer with greater visual comfort. A variety of methods have been disclosed for tinting such lenses. According to U.S. Pat. No. 4,891,046, the contents of which are incorporated by reference herein, a hydrophilic contact lens is tinted with a dichlorotriazine dye in a two step procedure. In the first step of the procedure, the lens, which is formed from a hydrophilic polymer obtained by the peroxide-initiated polymerization of a polymer-forming composition containing a hydroxyl group-containing acrylic ester monomer, e.g., hydroxyethyl methacrylate (HEMA), and N-vinylpyrrolidone, is immersed in an aqueous solution of dichlorotriazine dye maintained at an approximately neutral pH which reduces to near zero the rate at which the dye hydrolyzes or reacts with the hydroxyl groups of the acrylic ester monomer. Under these conditions, the dye diffuses into the lens. Thereafter, the dye-impregnated lens is immersed in an aqueous solution of base which catalyzes the reaction of the dye with the hydroxyl groups in the polymer backbone.
The hydrophilic contact lens tinting method of U.S. Pat. No. 4,891,046 is intended to be practiced on a finished lens and incorporates the dichlorotriazine dye in the hydrophilic polymer constituting the lens body in an operation which is entirely distinct from that used for forming the polymer.